Azlactone-containing pressure-sensitive adhesives

ABSTRACT

Pressure-sensitive adhesives are prepared by the simultaneous polymerization of minor amounts of at least one alkenyl azlactone monomer and at least one arylic-functional carboxylic acid monomer, or precursors thereof, with a major amount of at least one acrylic monomer. The pressure-sensitive adhesives, after application to a substrate, will significantly increase in adhesion to the resultant bonded substrate after they are in the bonded configuration.

This is a division of application Ser. No. 504,213 filed June 14, 1983,now abandoned.

DESCRIPTION

1. Field of the Invention

The present invention relates to pressure-sensitive adhesives and tapearticles prepared therefrom. The adhesives are derived from both analkenyl azlactone and an acrylic-functional carboxylic acid monomer orprecursors thereof as well as a major amount of anethylenically-unsaturated monomer.

2. Background of the Invention

Pressure-sensitive adhesive tapes are well known in the art. An"adhesive", as defined by G. G. Hawley in "The Condensed ChemicalDictionary", 9th Edition, Van Nostrand Reinhold: New York (1977), is"any substance, inorganic or organic, natural or synthetic, that iscapable of bonding other substances together by surface attachment". Apressure-sensitive adhesive (PSA) is generally a component of apressure-sensitive tape which in its most simple configuration iscomprised of the adhesive and a backing, and the overall construction istacky and adherent at the use temperature (typically room temperature)and adheres to a variety of substrates using only moderate (typicallyfingertip) pressure to form the bond. In this fashion,pressure-sensitive tapes constitute a complete, self-contained bondingsystem.

A good pressure-sensitive adhesive, according to D. W. Aubrey in"Developments in Adhesives", ed. W. C. Wake, Vol. 1, Chapter 5, AppliedScience Publishers, London (1977), must fulfill three main technicalrequirements:

1. The adhesive must exhibit adequate resistance to shear under theinfluence of an applied load; this relates to the adhesive's cohesion.

2. The adhesive must conform quickly to the surface to which it isapplied in order to rapidly form a bond; this relates to tack.

3. The adhesive must display adequate resistance to separation bypeeling once the bond is formed; this requirement relates to adhesion.

These three requirements are assessed generally by means of tests whichare designed to measure cohesion (shear holding power), tack, andadhesion (peel strength). These measurements taken together constitutethe "balance of properties" often used to characterize PSA's.

Of the parameters that have relevance for a PSA in the bonded condition,namely cohesion and adhesion, numerous methods have been developed forincreasing cohesion of PSA's subsequent to preparation and coating ofthe adhesive, e.g., various crosslinking reactions. Adhesion, on theother hand, can as a rule be controlled only at the stage of adhesivepreparation. Adhesion is influenced by bulk viscoelastic behavior(related to the polymer glass transition temperature, Tg) andinterfacial attractive forces between the adhesive and substrate. Thesefactors are regulated by the choice and ratio of the starting monomers.Thus, beyond the typical, modest build in adhesion observed fairly soonafter bonding which results from flow or creep of the polymeric adhesiveinto a condition of more complete contact with the substrate surface, noeffective measures have been developed to significantly increaseadhesion in the bonded condition.

Copolymers derived from alkenyl azlactone and acrylic-functionalcarboxylic acid monomers have been prepared and disclosed in BritishPat. No. 1,121,418 and U.S. Pat. No. 3,583,950. Both of these patentsincorporate an alkenyl azlactone monomer in a copolymer expressly forthe purpose of ultimately crosslinking the copolymer. These patentsbroadly teach the use of the crosslinkable, solid azlactone copolymersderived from at least three monomers in admixture with a suitablecrosslinking agent (e.g., a diol or diamine) as "coating compositions".A limited expansion upon this proposed utility is found in column 5,lines 16-20, of U.S. Pat. No. 3,583,950, wherein it is stated that "themixtures of the invention have a potlife sufficient to use them ascoating or impregnating agents, as adhesives, or--optionally togetherwith fillers--as patching materials." No mention is made of thepossibility of utilizing azlactone-containing copolymers themselves asadhesives.

Normally tacky, pressure-sensitive acrylate copolymer adhesives aredisclosed in U.S. Pat. (reissue) No. 24,906.

SUMMARY OF THE INVENTION

Briefly, the present invention provides a pressure-sensitive adhesivewhich, after application to a substrate, will significantly increaseadhesion to the resultant bonded substrate after it is in the bondedconfiguration.

The present invention is based on the unexpected discovery thatinterpolymers of (a) certain acrylate monomers, (b) at least oneacrylic-functional carboxylic acid monomer, and (c) at least one alkenylazlactone monomer undergo a dramatic increase in adhesion (compared tothe initial adhesion) in the bonded configuration. The dramatic increasein adhesion observed upon curing in the interpolymer of the invention isbelieved to be previously unknown in the art. Pressure-sensitiveadhesives, and articles such as tapes, of this invention increase theirlevel of adhesion, i.e., cure to greater than 55 percent (as measured bya peel adhesion test), preferably greater than 65 percent, and mostpreferably greater than 100 percent of the initially recorded valueafter one to three weeks in the bonded configuration, or more rapidlywhen the bond is subjected to elevated temperatures. In contrast,conventional pressure-sensitive adhesives and tapes exhibit only modestincreases in adhesion, if any at all. In fact, it is desirable in manyPSA tape uses to avoid any increase in adhesion.

Tape products of the invention thus have utility not only inapplications where very high adhesion values are desired but also wherethe initially applied adhesive is desired to be removed for purposes ofre-mounting or re-positioning. Once in place in the exact positiondesired, the adhesion will increase to such an extent that subsequentremoval is very difficult or even impossible without damaging one orboth of the substrate and backing.

The patents referenced above relating to azlactones deal exclusivelywith crosslinking an azlactone-containing interpolymer in the presenceof a crosslinking agent to achieve the ultimately desired properties. Acrosslinking agent is not added to the interpolymer in the presentinvention and is, in general, not desirable because the adhesionproperties of the resultant pressure-sensitive adhesive and the dramaticincrease in adhesion are adversely affected. Additionally, all theinterpolymers of the examples in the cited patents containing anacrylic-functional carboxylic acid monomer possess calculated Tg's ofroom temperature (20°-25° C.) or higher. Those skilled in the art of PSAformulation know that a useful PSA possesses a Tg that is at least 40°C. lower than the contemplated use temperature. Therefore, for PSA'sused at room temperature, the interpolymer Tg should be less than -15°C. for adequate tack to be present. It is clear that the patentees didnot contemplate use of their disclosed polymers as PSA's.

In the present application:

"interpolymer" means the product of the simultaneous polymerization oftwo or more dissimilar monomers. The term "interpolymer" is used indescribing the invention as opposed to "copolymer" which has beenutilized in the prior art in some instances to describe the polymerresulting from the simultaneous polymerization of only two dissimilarmonomers and in other instances of two or more than two dissimilarmonomers;

"bonded configuration" means a pressure-sensitive adhesive in itsend-use situation, i.e., when it adheres a tape backing or another solidobject to a substrate; and

"alkenyl azlactone" means a compound selected from the class consistingof 2-alkenyl-1,3-oxazolin-5-ones (also called 2-alkenyl-5-oxazolones inthe literature), 2-alkenyl-5,6-dihydro-4H-1,3-oxazin-6-ones, and2-alkenyl-4,5,6,7-tetrahydro-1,3-oxazepin-7-ones.

DETAILED DESCRIPTION AND SPECIFICATION OF THE INVENTION

The invention provides novel pressure-sensitive adhesives prepared bythe simultaneous polymerization of minor amounts of at least one alkenylazlactone monomer and at least one acrylic-functional carboxylic acidmonomer, or precursors thereof, with a major amount of at least oneacrylic monomer, the interpolymer exhibiting a glass transitiontemperature (Tg) of less than -15° C. The pressure-sensitive adhesivesof the invention are interpolymers formed from 100 molar parts ofethylenically-unsaturated monomers which comprise (1) from about 70 to90 molar parts of monomers consisting of

(a) 75-100 mole percent of an acrylic acid ester of at least onenon-tertiary alkyl alcohol, the molecules of said alcohol containing1-14 carbon atoms, the average being about 5-12 carbon atoms, and

(b) 15-0 mole percent of at least one monomer selected from the groupconsisting of vinyl acetate, styrene, vinyl ethers, and alkylmethacrylates, the alkyl group having 1 to 14 carbon atoms, and

(c) 10-0 mole percent of at least one monomer selected from the groupconsisting of acrylamide, methacrylamide, acrylonitrile,methacrylonitrile, and N-vinyl pyrrolidone, and

(2) from 25 to 5 molar parts of at least one alkenyl azlactone monomerhaving the formula I ##STR1## where R¹ is hydrogen or methyl; R² isselected from a single bond, --R³ --, and ##STR2## in which R³ is analkylene group having 1 to 12 carbon atoms, preferably 1 to 6 carbonatoms, and W is --O--, --S--, or --NH--; R⁴ and R⁷ are independentlyselected from a single bond, methylene, and substituted methylene having1 to 12 carbon atoms; R⁵ and R⁶ are independently alkyl or cycloalkylhaving 1 to 12 carbon atoms, aryl or aralkyl having 6 to 12 carbonatoms, or R⁵ and R⁶ taken together with the carbon to which they arejoined form a 5- or 6-membered carbocyclic ring, or R⁵ and R⁶ each maybe hydrogen when at least one of R⁴ and R⁷ is methylene; optionally, R³,R⁴, R⁵, R⁶ and R⁷ can be substituted by one or more groups which areunreactive with the azlactone ring, such as alkyl having 1 to 12 carbonatoms, halo, cyano, ether, ester, keto, silyl, and sulfide, thecarbon-containing substituent groups having up to 12 carbon atoms; and

(3) from about 25 to 5 molar parts of at least one acrylic-functionalcarboxylic acid monomer, or precursors thereof. Acrylic-functionalcarboxylic acid monomers include acrylic acid, methacrylic acid,itaconic acid, maleic acid, and an N-acryloylamino acid.Acrylic-functional carboxylic acid monomer precursors include monomerswhich can be incorporated into a polymer structure and subsequentlyconverted, for example by thermolysis, into an acrylic-functionalcarboxylic acid monomer unit. For example, a precursor to acrylic acidis tetrahydropyranyl acrylate whose preparation and conversion isdescribed in Canadian Pat. No. 672,947 which is incorporated herein byreference.

As has been mentioned, the Tg of the interpolymer is critical to itsutilization as a PSA, with a Tg of less than -15° C. being required forapplication at room temperature. Specific, useful combinations of theabove monomers can be computed by application of Equation (1) [obtainedfrom W. R. Sorenson and T. W. Campbell's text entitled "PreparativeMethods of Polymer Chemistry", Interscience: New York (1968), p. 209].Specific values for Tg's of appropriate ##EQU1## wherein Tg=glasstransition temperature for the interpolymer

Tgi=glass transition temperature for the homopolymer of the ith monomer

Wi=weight fraction of the ith monomer

homopolymers were obtained, or were estimated from related polymers,from W. A. Lee and R. A. Rutherford's chapter in "Polymer Handbook", 2ndedition, edited by J. Brandrup and E. H. Immergut, Wiley: New York(1975), pp. III-139 through III-192. Specific values for alkenylazlactone homopolymers, not included in the previous reference, wereobtained from L. D. Taylor, et al., J. Polymer Sci.: Polymer Lett., 9,187 (1971).

The acrylic monomers that comprise the major portion of the monomercharge and are commonly utilized in acrylic pressure-sensitive adhesivesare described in U.S. Pat. Re. No. 24,906, which patent is incorporatedherein by reference. Examples of such monomers include iso-amylacrylate, n-hexyl acrylate, heptyl acrylate, n-octyl acrylate, iso-octylacrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, undecylacrylate, dodecyl acrylate, tridecyl acrylate, and tetradecyl acrylate.A preferred embodiment of the present invention utilizes an acrylic acidester derived from a branched eight-carbon alcohol, i.e., 2-ethylhexylacrylate or iso-octyl acrylate, alone as the 70-90 mole percent monomer.Other unsaturated monomers defined above in (1)(b) and (1)(c) may beutilized to specifically adjust the adhesion, tack, and cohesion thatmake up the balance of properties of the initially appliedpressure-sensitive adhesive, but they are not involved in the unusualadhesion increasing phenomenon specifically addressed in the invention.

The alkenyl azlactone monomers useful in the present invention aredescribed in U.S. Pat. No. 4,304,705, which is incorporated herein byreference. Preferred alkenyl azlactone monomers include:

2-vinyl-4,4-dimethyl-1,3-oxazolin-5-one,

2-isopropenyl-4,4-dimethyl-1,3-oxazolin-5-one,

2-vinyl-4-ethyl-4-methyl-1,3-oxazolin-5-one,

2-vinyl-4,4-diethyl-1,3-oxazolin-5-one,

2-vinyl-4-iso-butyl-4-methyl-1,3-oxazolin-5-one,

2-vinyl-4-methyl-4-phenyl-1,3-oxazolin-5-one,

2-vinyl-4,4-diphenyl-1,3-oxazolin-5-one,

2-vinyl-4,4-pentamethylene-1,3-oxazolin-5-one,

2-vinyl-4,4-tetramethylene-1,3-oxazolin-5-one, and

2-vinyl-4,4-dimethyl-1,3-oxazin-6-one.

Preferred acrylic-functional carboxylic acids include acrylic acid,methacrylic acid, and the N-acryloylamino acids (disclosed in U.S. Pat.No. 4,157,418, which is incorporated herein by reference) such asN-acryloylglycine, N-methacryloylglycine, N-acryloylaspartic acid, andN-acryloyl-N-(2-cyanoethyl)glycine.

The interpolymers of the invention can be prepared by employingconventional solution or bulk polymerization techniques, preferablyusing organic solvents such as ethyl acetate, toluene, xylene, acetone,methyl ethyl ketone, acetonitrile, and tetrahydrofuran, as are describedin U.S. Pat. No. 4,304,705. Alcohol solvents and chain transfer agentsshould be avoided since they react with the azlactone ring. A preferredmethod of preparing the interpolymer solutions of the invention is byphotopolymerization in the absence of solvent. This method is applicablewhen the monomers form a solution at the polymerization temperature(typically room temperature, e.g., 20°-25° C.) and is generallydescribed in U.S. Pat. No. 4,181,752, which method is incorporatedherein by reference.

The interpolymer solutions of the invention that are prepared byconventional solution polymerization techniques are transformed into thepressure-sensitive adhesives and tapes of the invention by coating (bymethods well-known in the art such as knife coating, bar coating, dipcoating, roll coating, gravure coating, curtain coating, spray coating,and the like) the viscous solution containing the interpolymer onto abacking, and subsequently removing the solvent, e.g., by heating. This,of course, does not apply to interpolymers of the invention that areprepared in the absence of solvent, i.e., in bulk, utilizing thephotopolymerization method, in which the monomer mixture is similarlycoated onto the desired backing and polymerized in a tape configuration.The thickness of the dry coating can vary from 0.01 to 10 mm or moredepending on the nature of the intended use for the adhesive.

The tape backing may be of two kinds: permanent and non-permanent. Apermanent backing is one in which it is desired that the backing remainwith the pressure-sensitive adhesive in the bonded configuration. Usefulpermanent backings are metals such as aluminum, steel including thevarious alloys, and copper; cloth; paper; polymeric films such aspoly(ethylene terephthalate), poly(carbonates), poly(acrylates),poly(methacrylates), poly(olefin), and poly(cellulose acetate); andglass which includes glass reinforced composites. As is well known toone skilled in the art, various priming agents and surface treatmentscan be utilized to facilitate adhesion between the pressure-sensitiveadhesive and the permanent backing. A non-permanent backing is one inwhich the pressure-sensitive adhesive is intended to be only temporarilybonded thereto, to facilitate transfer of the pressure-sensitiveadhesive to a substrate. Once the pressure-sensitive adhesive has beenadhered to the substrate, the non-permanent backing can be removed andanother substrate can be bonded to the original substrate via thepressure-sensitive adhesive. Useful non-permanent backings include paperor polymeric films that have been surface-coated with various releasecoatings that are well known in the art such as silicone coatingsdisclosed in U.S. Pat. Nos. 3,061,567 and 4,216,252 that facilitate thetransfer of the pressure-sensitive adhesive.

One aspect of the novelty of the present invention is that once thepressure-sensitive adhesives are in place in the bonded configurationthe adhesion level between the adhesive and substrate(s) increasesdramatically. This adhesion increasing phenomenon derives from thealkenyl azlactone and acrylic-functional carboxylic acid portions of thepressure-sensitive adhesives. It has been found that the increase inadhesion does not occur when one or the other of these two kinds ofmonomers is omitted.

In the present invention, it appears that the dramatic increase inadhesion derives from one or a combination of the following reactions:

1. Reaction of the azlactone groups on the pressure-sensitive adhesiveoccurs with nucleophilic groups that may be present on the substratesuch as --OH, --SH, or --NHR⁸, where R⁸ is --H or a lower alkyl groupcontaining 1 to 4 carbon atoms. Such a reaction is shown in Equation (2)and results in formation of a very strong covalent bond between theadhesive and the substrate, thus accounting for the increase inadhesion. ##STR3## wherein ○ denotes the remainder of theazlactone-containing interpolymer, and R⁴, R⁵, R⁶, and R⁷ are definedabove.

2. The reaction of the azlactone groups on the pressure-sensitiveadhesive with water that is adsorbed on the surface of the substrateoccurs, providing an adhesive with a higher modulus and groups that canbetter interact with the substrate as shown in Equation (3). ##STR4##

This hydrolysis has been confirmed by infrared measurements on thefilms. The generation of the amido-functional carboxylic acid (II) wouldresult in a dramatic increase in modulus or stiffness of the adhesivebecause of the very much more strongly interactive nature, i.e.,hydrogen bonding, of the polar amide and acid groups compared to theazlactone precursor. This kind of cohesion building effect wouldcertainly effect the peel adhesion which is directly related to themodulus of the bonded adhesive. Furthermore, and perhaps moreimportantly as discussed above, adhesion is related also to interfacialattractive forces, and these would be expected to be dramaticallyincreased upon generation of the strongly interactive acid and amidegroups, especially at the adhesive-substrate interface.

3. The ring-opening hydrolysis of the azlactone ring as depicted inEquation (3) is believed to take place resulting in a net expansion involume. According to measurements withpoly(2-vinyl-4,4-dimethyl-1,3-oxazolin-5-one) and the hydrolyzedhomopolymer, poly(N-acryloylmethylalanine), both polymers haveapproximately the same density. Thus, when mass (in the form of reactedwater) is added to the system via the ring-opening hydrolysis reaction,the result is an increase in volume. The manifestation of this resultfrom an adhesive standpoint is that an increase in adhesion will resultfrom a mechanical locking of the adhesive to the substrate's surface,especially in those regions of the surface of the substrate that mightbe roughened or in any way have some irregularities, e.g., cracks, pits,and the like, present. In this manner, the adhesive increase would bevery much like removing expanded, frozen water, i.e., ice, from a carwindshield, which is, of course, a difficult removal problem.

The function of the acrylic-functional carboxylic acid monomer portionof the pressure-sensitive adhesive would be as a catalyst for thering-opening reaction with a nucleophilic substrate and/or water. Thecatalytic function of the acid is believed to involve protonation of thering nitrogen, as shown in Equation (4), ##STR5## and, in the process,producing intermediate III which would be more susceptible tonucleophilic attack than the unprotonated azlactone ring.

The PSA's of the present invention are useful in any bonding applicationwhere it may be desirable to be able to realign the joined surfaces. Therate at which the adhesion increasing event occurs, i.e., curing, isdirectly proportional to the temperature of the bond, and thus can beregulated at the discretion of the user. At room temperature the buildmay require from one to three weeks to eventually reach the maximumvalue. When the bond is subjected to elevated temperatures, e.g.,90°-100° C., the adhesion maximum is usually achieved in less than anhour. The temperatures and times required are somewhat variable anddepend on the particular substrate and amount of moisture present.

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention.

All of the EXAMPLES utilize the following materials and methods:

MONOMERS

Iso-octyl acrylate (hereinafter abbreviated as IOA) was prepared fromiso-octyl alcohol (available from the Exxon Corporation, Chicago, Ill.)and acrylic acid (abbreviated as AA, available from Aldrich ChemicalCompany, Milwaukee, Wis.) by well-known esterification procedures; thewater-white fraction distilling at 99°-100.5° C./11 mm was collected. Ina similar fashion 2-methylbutyl acrylate (MBA) was prepared from2-methylbutanol (Union Carbide Corp., Danbury, Conn.) and distilled at91° C./100 mm. 2-Ethylhexyl acrylate (EHA) (Aldrich Chemical Co.,Milwaukee, Wis.) and lauryl methacrylate (LMA) (Aldrich Chemical Co.)were commercial samples that were passed through silica gel prior touse.

The alkenyl azlactone monomers were synthesized according to the methodof L. D. Taylor, et al., Polymer Letters, 9, 187 (1971), which is hereinincorporated by reference. The 2-vinyl-4,4-dimethyl-1,3-oxazolin-5-onemonomer (hereafter abbreviated as VDM) distilled at 26°-28° C./0.6 mm,and the 2-vinyl-4,4-pentamethylene-1,3-oxazolin-5-one (designated VPM)distilled at 71°-74° C./0.3 mm. The2-vinyl-4,4-dimethyl-1,3-oxazin-6-one (VDO) was prepared using thedicyclohexylcarbodiimide method described in U.S. Pat. No. 4,304,705.The water-white liquid distilled at 77°-78° C./6.3 mm. The identity ofthe compound was established by spectral and elemental analyses.

The N-acryloylaspartic acid (AAS) was prepared according to the methodof S. Heilmann, et al., J. Appl. Polymer Sci., 24, 1551 (1979).

All ratios are given as mole percents. Tg's were calculated according toEquation (1), and Examples of the invention exhibited values between-18° C. and -53° C.

COATABLE SYRUPS

When the photopolymerization method is utilized, it is necessary thatthe polymerizable monomer solution have sufficient viscosity to besuitably substantive for coating purposes. Otherwise, as is known tothose skilled in the art, the monomer mixture does not coat the backinguniformly and will exhibit undesirable running and flowing after coatingand before exposure to the polymerizing light. In order to obtaincoatable syrups from the monomer solution, to each monomer mixture wasadded a photo-initiator such as Irgacure™ 651 (0.25 weight percent basedon the monomer mixture; available from the Ciba-Geigy Corporation,Ardsley, N.Y.), and the resulting solution was sparged briefly with aninert gas such as nitrogen, argon, or carbon dioxide, to remove oxygen.Then the colorless solution in a glass vessel, transparent to theactinic radiation, was exposed to the light from a bank of fourfluorescent Blacklight (available from GTE Sylvania Incorporated,Danvers, Mass.) bulbs at a vessel-to-bulb distance of 10 cm. A preferredglass vessel was an ordinary colorless glass, laboratory jar or bottlewith a screw cap. In order to achieve efficient mixing it was desirableto place the vessel on a laboratory ball mill roller under a bank oflights. Within 5-10 minutes the solution usually became noticeablythickened, and the exposure was stopped when a Brookfield viscosity (asmeasured with a Brookfield Viscometer, available from BrookfieldEngineering Laboratories, Inc., Stoughton, Mass.) of 2000-3000centipoises was achieved. This increase in viscosity was accompaniedtypically by a conversion of 7-10 weight percent of monomers to aninterpolymer. The homogeneous coating syrups thus produced were utilizeddirectly to prepare the interpolymers of the invention.

PHOTOPOLYMERIZATION AND TESTING CONDITIONS

The specific conditions of photopolymerization are described in U.S.Pat. No. 4,181,752 (Light Source A). All coatable syrups wereknife-coated onto polyester film (15 cm wide and 0.05 mm in thickness)at a thickness of 0.05 mm. The resulting pressure-sensitive tapes wereslit into 1.25 cm widths for testing. The 180° Peel Adhesion wasmeasured according to ASTM D3330-80 (Method A for single-coated tapes).The average of three separate trials was utilized in all cases todetermine the percent change in peel adhesion.

EXAMPLE 1

Pressure-sensitive tapes consisting of IOA-AA-VDM (73:13.5:13.5)(Tg=-48° C.) were prepared using the photopolymerization methoddescribed above and were applied to two stainless steel panels. The peeladhesion from one of the panels was recorded immediately, while theother panel was allowed to stand at room temperature for a period of oneweek. The resulting increase in peel adhesion of the tape on the panelthat was allowed to stand one week relative to the sample that wasmeasured immediately was 120 percent.

EXAMPLES 2-7

The pressure-sensitive tapes of these EXAMPLES were prepared as inEXAMPLE 1 and each was applied to two stainless steel panels as above,and one each of the panels was heated for 30 minutes at 93° C. toaccelerate the increase in peel adhesion. After cooling for one hour,the adhesion values were measured and compared with the initial values.The results are given in TABLE I.

                                      TABLE I                                     __________________________________________________________________________                                           Percent                                Ex.                                    increase in                            No. IOA MBA  AA   VDM  VPM  VDO  Tg (°C.)                                                                     adhesion                               __________________________________________________________________________    2   80  --   10   10   --   --   -53   110                                    3   75  --     12.5                                                                               12.5                                                                             --   --   -49   100                                    4   75  --   10   15   --   --     -48.5                                                                              90                                    5   75  --     12.5                                                                             --     12.5                                                                             --   -45   150                                    6   70  --   15   --   --   15   -45    92                                    7   --  80   10   10   --   --   -18    81                                    __________________________________________________________________________

The data of TABLE I show that all interpolymers exhibited a significantbuild in adhesion upon being heated for 30 minutes at 93° C.

EXAMPLE 8

An EHA/LMA/AAS/VDM (55/25/5/15) interpolymer (Tg=-41° C.) was preparedby solution polymerization in dry acetone (0.4 weight fraction ofmonomers to solvent), using azobis(isobutyronitrile) (0.5 weightpercent) as initiator, at 55° C. for 24 hours. Tapes with a dry coatingthickness of 0.05 mm were prepared by coating the solution polymer ontochromated aluminum (0.05 mm) and removing the solvent at 88° C. for 10minutes. The pressure-sensitive tapes were applied to two stainlesssteel panels. The peel adhesion from one of the panels was recordedimmediately. The second panel was heated for 30 minutes at 93° C. Aftercooling for one hour, the peel adhesion value was measured and comparedto the initial value, giving a percent increase in adhesion of 61percent.

COMPARATIVE EXAMPLES 1-5

The novelty and dramatic increase in peel adhesion of present inventionpressure-sensitive tapes are demonstrated by comparison to increases inpeel adhesion of similarly applied and treated commercialpressure-sensitives tapes shown in TABLE II. The comparative examples ofcommercial pressure-sensitive tapes were applied to two panels and onepanel heated as described in EXAMPLES 2-7.

                  TABLE II                                                        ______________________________________                                        Comparative                       Percent                                     example   Source of   Adhesive    increase in                                 number    tape (3M)   type        adhesion                                    ______________________________________                                        C1        Tape #468   Acrylic     53                                          C2        Transparent Acrylic     8                                                     tape #810                                                           C3        Filament    Natural rubber                                                                            0                                                     tape #898                                                           C4        Box sealant Kraton ®                                                                              3                                                     tape #355                                                           C5        Tape #8402  Silicone    8                                           ______________________________________                                    

The data of TABLE II show that the adhesion increase was highly variableand none of the commercial tapes approached the tapes of the inventionin degree of adhesion increase.

EXAMPLE 9

This example shows the effect of moisture on the adhesion increasingphenomenon. An IOA-AA-VDM (70:15:15) interpolymer (Tg=-45° C.) wasprepared from carefully dried monomers (stored over 4 Å molecularsieves) by solution polymerization in dry ethyl acetate (0.4 weightfraction of monomers to solvent), using azobis(iso-butyronitrile)(available from the E.I. DuPont Co., Wilmington, Del.) (0.5 weightpercent) as initiator, at 55° C. for 24 hours. Tapes were prepared bycoating the solution polymer onto the polyester film (at a thickness of0.05 mm) and removing the solvent by heating at 88° C. for 10 minutes.Tapes were applied to two sets of stainless steel plates: one set whichhad been equilibrated for 24 hours at room temperature and 0 percentrelative humidity, and a second set which had been equilibratedsimilarly at 90-100 percent relative humidity. The 180° peel adhesionswere measured initially and after heating on the substrate at 65° C. for3 hours. Adhesion to the "dry" (0 percent R.H.) substrate increased byonly 27 percent whereas adhesion to the "wet" (90-100 percent R.H.)substrate had increased by 106 percent.

EXAMPLE 10

This example demonstrates that the net expansion in volume that occurswhen the azlactone rings hydrolyze may be important in the build inadhesion.

An IOA-AA-VDM (70:15:15) interpolymer (Tg=-45° C.) was prepared as inEXAMPLE 9. The interpolymer solution was diluted with ethyl acetate to25 percent solids (w/w) and divided into two portions.

One portion was coated (at a thickness of 0.05 mm) onto chromatedaluminum (Alodine™ 1200, 0.05 mm thick; available from Amchem Products,Inc., Ambler, Pa.) with a dry coating thickness of 0.025 mm. This"unhydrolyzed" interpolymer was applied to a stainless steel plate, andthe peel adhesion was recorded initially and after heating at 93° C. for30 minutes. The resultant increase in peel adhesion relative to theunheated sample was 67 percent.

To the other portion, a stoichiometric excess of water andethanesulfonic acid catalyst (0.05 weight percent) were added, and themixture was heated at 55° C. for 20 hours. Infrared analysis of films ofthe interpolymer showed that the azlactone groups had all reacted withthe water. This "hydrolyzed" interpolymer exhibited only a 12 percentincrease in peel adhesion.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth herein.

We claim:
 1. A pressure-sensitive adhesive tape comprising(a) a tapebacking, and (b) coated on at least one surface thereof apressure-sensitive, normally-tacky, adhesive interpolymer which is theproduct of simultaneous polymerization of ethylenically-unsaturatedmonomers which comprise(1) from about 70 to 90 molar parts of monomersconsisting of (a) 69-100 mole percent of an acrylic acid ester of atleast one non-tertiary alkyl alcohol, the molecules of said alcoholcontaining 1-14 carbon atoms, the average being 5-12 carbon atoms, (b)31-0 mole percent of at least one monomer selected from the groupconsisting of vinyl acetate, styrene, vinyl ethers, and alkylmethacrylates, the alkyl group having 1 to 14 carbon atoms, and (c) 10-0mole percent of at least one monomer selected from the group consistingof acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, andN-vinyl pyrrolidone, and(2) from 25 to 5 molar parts of at least onealkenyl azlactone monomer having the formula I ##STR6## where R¹ ishydrogen or methyl; R² is selected from a single bond, --R³ --, or##STR7## in which R³ is a substituted or unsubstituted alkylene grouphaving 1 to 12 carbon atoms, and W is --O--, --S--, or --NH--; R⁴ and R⁷are independently selected from a single bond, methylene, or substitutedmethylene having 1 to 12 carbon atoms; R⁵ and R⁶ are independentlysubstituted or unsubstituted alkyl or cycloalkyl having 1 to 12 carbonatoms, aryl or aralkyl having 6 to 12 carbon atoms, or R⁵ and R⁶ takentogether with the carbon to which they are joined forming a 5- or6-membered carbocyclic ring or R⁵ and R⁶ each may be hydrogen when atleast one of R⁴ and R⁷ is methylene; and (3) from 25 to 5 molar parts ofat least one acrylic-functional carboxylic acid monomer selected fromacrylic acid, methacrylic acid, itaconic acid, maleic acid, or anN-acryloylamino acid; said interpolymer exhibiting a glass transitiontemperature (Tg) of less than -15° C.
 2. The pressure-sensitive adhesivetape according to claim 1 wherein said ethylenically-unsaturated monomerof component (1) (a) of said interpolymer is an acrylic acid esterderived from an 8-carbon alcohol.
 3. The pressure-sensitive adhesivetape according to claim 1 wherein said monomer component of saidinterpolymer is selected from the group consisting of (1) (a) components2-ethylhexyl acrylate, iso-octyl acrylate, and 2-methylbutyl acrylate,and (1) (b) component lauryl methacrylate.
 4. The pressure-sensitiveadhesive tape according to claim 1 wherein said alkenyl azlactonemonomer component of said interpolymer is selected from the groupconsisting of2-vinyl-4,4-dimethyl-1,3-oxazolin-5-one,2-vinyl-4,4-pentamethylene-1,3-oxazolin-5-one, and2-vinyl-4,4-dimethyl-1,3-oxazin-6-one.
 5. The pressure-sensitiveadhesive tape according to claim 1 wherein said acrylic-functionalcarboxylic acid monomer component (3) of said interpolymer is selectedfrom the group consisting of acrylic acid, methacrylic acid, andN-acryloylaspartic acid.
 6. The pressure-sensitive adhesive tapeaccording to claim 1 wherein said acrylic-functional carboxylic acidmonomer component (3) of said interpolymer is replaced by a precursorthereof.
 7. The pressure-sensitive adhesive tape according to claim 1wherein said interpolymer component (1) (a) is iso-octyl acrylate,component (2) is 2-vinyl-4,4-diethyl-1,3-oxazolin-5-one, and component(3) is acrylic acid.
 8. The pressure-sensitive adhesive tape accordingto claim 1 wherein component (1) (a) is iso-octyl acrylate, component(2) is 2-vinyl-4,4-pentamethylene-1,3-oxazolin-5-one, and component (3)is acrylic acid.
 9. The pressure-sensitive adhesive tape according toclaim 1 wherein R³, R⁴, R⁵, R⁶ and R⁷ of said alkenyl azlactone monomercomponent of said interpolymer are substituted by one or more groupsselected from alkyl having 1 to 12 carbon atoms, halo, cyano, ether,ester, keto, silyl, and sulfide, the carbon-containing substituentgroups having up to 12 carbon atoms.
 10. The pressure sensitive adhesivetape according to claim 1 in which said pressure-sensitive adhesiveinterpolymer has been cured.
 11. A pressure-sensitive adhesive tapecomprising:a. a tape backing, and b. coated on at least one surfacethereof a pressure-sensitive adhesive interpolymer which is the reactionproduct of ethylenically-unsaturated monomers which comprise(1) fromabout 70 to 90 molar parts of monomers consisting of(a) 75-100 molepercent acrylic acid ester of at least one non-tertiary alkyl alcohol,the molecules of said alcohol containing 1-14 carbon atoms, (b) 15-0mole percent of at least one monomer selected from the group consistingof vinyl acetate, styrene, vinyl ethers, and alkyl methacrylates, thealkyl group having 1 to 14 carbon atoms, and (c) 10-0 mole percent of atleast one monomer selected from the group consisting of acrylamide,methacrylamide, acrylonitrile, methacrylonitrile, and N-vinylpyrrolidone, and (2) from 25 to 5 molar parts of at least one alkenylazlactone monomer of the formula I ##STR8## where R¹ is hydrogen ormethyl; R² is selected from a single bond, --R³ --, or ##STR9## in whichR³ is a substituted or unsubstituted alkylene group having 1 to 12carbon atoms, and W is --O--, --S--, or --NH--; R⁴ and R⁷ areindependently selected from a single bond, methylene, or substitutedmethylene having 1 to 12 carbon atoms; R⁵ and R⁶ are independentlysubstituted or unsubstituted alkyl or cycloalkyl having 1 to 12 carbonatoms, aryl or aralkyl having 6 to 12 carbon atoms, or R⁵ and R⁶ takentogether with the carbon to which they are joined forming a 5- or6-membered carbocyclic ring, or R⁵ and R⁶ each may be hydrogen when atleast one of R₄ and R₇ is methylene; and (3) from 25 to 5 molar parts ofat least one acrylic-functional carboxylic acid monomer selected fromacrylic acid, methacrylic acid, itaconic acid, maleic acid, or anN-acryloylamino acid; said interpolymer exhibiting a glass transitiontemperature (Tg) of less than -15° C.
 12. The pressure-sensitiveadhesive tape according to claim 11 in which component b has been cured.